P441: DIFFERENCES IN GENE EXPRESSION PATTERN AND IMMUNOPHENOTYPE OF BONE MARROW MULTIPOTENT MESENCHYMAL STROMAL CELLS IN PATIENTS AT THE ONSET OF ACUTE LEUKEMIA AND AFTER ACHIEVING REMISSION
Authors: A. Sadovskaya, N. Petinati, N. Kapranov, N. Drize, A. Vasilieva, O. Gavrilina, E. Parovichnikova
Journal: HemaSphere (2022)

Background: The stromal microenvironment plays a key role in both maintaining normal hematopoiesis and assisting malignant cells during leukemia development. In patients with acute leukemia, the properties of multipotent mesenchymal stromal cells (MSCs) are changed both at the onset of the disease due to interaction with tumor cells and upon reaching remission due to chemotherapy. As a result, the ability of MSCs to maintain normal hematopoiesis is reduced. A detailed study of these changes may allow the development of rehabilitation measures for restoring the stromal microenvironment of patients. Aims: The aim of this work was to study general changes in gene expression pattern and immunophenotype of MSCs in patients with acute leukemia at the onset of the disease and in remission. Methods: The study included MSCs obtained from the bone marrow (BM) of 15 patients: 4 with ALL (1 male, 3 female, median age 26.5) and 11 AML (4 male, 7 female median age 33), BM of 30 donors of appropriate age was used as control. All donors and patients signed informed consent. MSCs were cultured by standard methods. Immunophenotypes were studied by flow cytometry. Relative expression levels (REL) of several genes were investigated by real time PCR. Results: The study of the mean fluorescence intensity (MFI) of MSC markers revealed a significant decrease in MFI of CD274 (PD-L1) in primary patients compared to healthy donors and its absence on the cells of patients in remission. At the onset both MFI of CD54 (ICAM-1) and the proportion of CD54+ MSCs were decreased. In remission these parameters decreased even more, so the treatment reduced the adhesive capacity of MSCs. The expression of CD105 was reduced at the onset of the disease and increased after the end of treatment, but did not normalize. In patients at the onset of the disease and in remission, compared with healthy donors, the expression of IL1R1, PDGFRβ, ANG1 was reduced; expression of IL6, PPARγ, JAG1, was increased (see Figure). Decreased level of IL8 and SOX9 normalized in remission. The decrease in growth factor (GF) receptors PDGFRβ and IL1R1 (IL1β may act as a GF for BM cells) in patients may be a result of negative feedback loops: GFs typically act as auto- and paracrine regulators, and malignant cells often overexpress various GF. The fact that these genes’ expression does not return to normal in remission may be a result of damage from treatment. IL1β expression in patients was not different from normal, but its increase in remission compared to onset implies stroma restoration processes. Another important effect is the alteration in MSCs’ interactions with stem cells: JAG1 product helps to ensure stem cells’ quiescent state and bond with stroma. In contrast, there is an increase in IGF1 expression at the onset, which can lead to stem cell activation. Alterations in the RELs of differentiation markers (SOX9, SPP1, PPARγ) indicate changes in the predisposition of MSCs to differentiation. PPARγ is a multifunctional nuclear receptor, and can inhibit proliferation. PPARγ upregulation may once again be a result of negative feedback networks preventing MSCs’ uncontrolled proliferation in GF-rich microenvironment. Image:Summary/Conclusion: The data suggest dramatic alterations in hematopoietic and stromal cells interaction at the onset of acute leukemia that were not undone by achieving remission. This is supported by decreased levels of endoglin and ICAM-1 and alteration of gene expression pattern. The materials supported by grants from the Russian Foundation for Basic Research project 19-29-04023 were used.